Fat as Fuel

Question 1

Biological functions of lipids

Answer 1

Components of cell membranes (phospholipids, cholesterol)
Hormone precursors (cholesterol => steroid) (Arachidonic acid=> prostaglandins)
Long term fuels (TAG)

Question 2

Efficiency of triglycerides as fuel

Answer 2

Compact storage
TAG as large fat droplets in fat cells of adipose tissue
Large body stores (11kg of fat on average adult)
The most energy dense energy source

Question 3

Structure of triglycerides

Answer 3

Glycerol

Fatty acids

Question 4

Names of common fatty acids

Answer 4

Formic acid C1
Acetic acid C2
Propionic acid C3
Butyric acid C4
Caprylic acid C8
Palmitic acid C16
Stearic acid C18
Oleic acid C18:1
Linoleic acid C18:2
Linolenic acid C18:3
Arachidic acid C20

Question 5

Breakdown of stored triglycerides in adipose tissue

Answer 5

TAG =triglycerol lipase=> FA + DAG
DAG =diglycerol lipase=> FA + MAG
MAG =monoglycerol lipase=> FA + G

Free FA travel in plasma bound to albumin
Glycerol diffuses in blood stream to all tissues

Question 6

What are G and FA used for

Answer 6

FA, fuel source for muscles, heart and liver

Both can be used in energy generation

Question 7

What is triglycerol lipase activated by?

Answer 7

Adrenaline and glucagon

Question 8

How is glycerol metabolised

Answer 8

Water soluble glycerol taken up by all tissues
Most tissue
enters glycolysis, coveted to pyruvate => TCA for oxidation to CO2

Liver in starvation
enters glycolysis, gluconeogenesis

Question 9

FA metabolism by B oxidation pathway

Answer 9

All reactions in mitochondrial matrix
Intermediates present as CoA thirsters
Biological energy of FA molecule conserved as transfer of
2H + NAD+/FAD => NADH + FADH2
4 enzyme reactants => removal of acetyl CoA

Question 10

Activation of LCFA

Answer 10

Fatty acids =CoA activating enzyme ATP=> Fatty acid CoA + AMP + PPi

Question 11

Coenzyme A, thioester bonds with carboxylic acids

Answer 11

Carboxylic acid + CoASH => Carboxylic acid SCoA + H2O

Question 12

Transport of fatty acids into mitochondria Stage 1

Answer 12

From cytosol to inter membrane space in mitochondria

Conversion of fatty acyl CoA and carnitine to carnitine fatty acyl and CoA in cytosol with carnitine palmitoyl transferase I

Fatty acyl carnitine can cross outer mitochondrial membrane

Question 13

Transport of fatty acids in to mitochondria Stage 2

Answer 13

From inter membrane space to inner mitochondrial matrix

Translocase transports fatty acyl carnitine in exchange for carnitine by fac diff through carnitine transporter

Carnitine palmitoyl transferase II in inner mitochondrial membrane catalyses transfer of acyl from fatty acyl carnitine to CoA => fatty acyl CoA and free carnitine

Free carnitine returned to inter membrane space via carnitine transporter

Fatty acyl CoA can be used in B oxidation to yield acetyl CoA

Question 14

Removal of 2H Reaction 1

Answer 14

Fatty acyl CoA =acyl coAdehydrogenase FAD=> Unsaturated Fatty acyl CoA + FADH2

FAD often used to form C=C

Question 15

Addition of water Reaction 2

Answer 15

Enoyl CoA=enoyl CoA hydrolase + H2O=> 3Lhydroxyacyl CoA

Question 16

Removal of 2H Reaction 3

Answer 16

3LhydroxyacylCoA =3LhydroxyacylCoA dehydrogenase + NAD+=> BketoacylCoA + NADH + H+

Oxidation reduces NAD

Question 17

Removal of 2C unit Reaction 4

Answer 17

BketoacylCoA =BketoacylCoA thiolase+ CoASH=> Fatty acyl CoA + Acetyl CoA

Fatty acyl CoA reenters cycle
Acetyl CoA enters TCA

Question 18

Overal B oxidation cycle

Answer 18

Fatty acyl CoA
-2H+
\+H2O
-2H
-2C unit

Question 19

Summary of B oxidation pathway with 16C fatty acid

Answer 19

Fatty acid with 16C atoms => repeats of B oxidation pathway, produce 7NADH + 7FADH2
Gives rise to 8 acetyl CoA => TCA cycle

Question 20

Energy yield from fatty acid oxidation (16C)

Answer 20

Fatty acid with 16C => 8 acetyl CoA
ATP yield = 8 x 10 ATP

7 repeats of B oxidation => 7NADH and 7FADH2

ATP yield = (7x2.5)+(7x1.5) -2 = 106

Question 21

Fate of odd chain fatty acids (propionyl CoA)

Answer 21

Enzyme requires cobalamin (B12)

Propionyl CoA =HCO3- ATP=> D methylmalonyl CoA <=> Lmethylmalonyl CoA <=B12=> Succinyl CoA

Question 22

Regulation of fat metabolism

Answer 22

Release of fatty acids from adipose tissue
adrenaline, glucagon activates lipase enzyme
Rate of entry into mitochondria via carnitine shuffle
Rate of reoxidation of cofactors NADH and FADH2 by cytochrome/respiratory chain

Question 23

Metabolic organ profiles of brain, muscle, adipose and liver

Answer 23

Brain uses exclusively glucose (KB) as it lacks glucose 6-phosphatase

Muscle fueled by glucose, FA (KB), lacks glucose 6 phosphatase

Adipose tissue, recevoir for TAG

Liver provides fuel for brain, muscle and other organs

Question 24

Names of common dietary fats (trans, unsat, sat)

Answer 24

Trans elaidic acid
Unsat oleic acid
Sat stearic acid